The invention refers to a method of recovering heavy oil from a section of an oil field containing strata of oil shale or tar sand. Deposits of heavy oil which comprise oil shale from which kerogen can be recovered or oil sand from which bitumen can be recovered feature in common the drawback that no natural gas pressure is present, which drives the matter to be recovered toward the ground surface. Presently said deposits of heavy oil are mined by conventional mining methods and usually the heavy oil is recovered by means of a retorting method in plants located distant from said heavy oil deposits. This procedure is extremely costly, specifically because the mined crude rock must be transported from the respective heavy oil deposit to the processing plant and thereafter the depleted residues must be again transported back for a depositing thereof or must be transported to a different location.
Several methods by means of which the recovering of the heavy oil can be carried out directly at the location of the deposits have been proposed.
In U.S. Pat. No. 2,757,738 (Ritchey) sections of oil fields are heated by means of radio frequency waves to render the heavy oil flowable for the recovery thereof. However, this method has not succeeded in practice because the local heating in the area surrounding immediately the electrodes in order to generate the radio frequency waves has been to such a large extent that a coking of the crude oil occurred.
It is proposed in U.S. Pat. No. 3,538,488 to treat sections of oil fields by means of inserted steam to render the heavy oil flowable. However, this method is often impeded by the phenomenon that the steam following the path of the least resistance blows through from one bore hole to another bore hole such that only a limited section of the heavy oil containing strata is heated. Then, only a small percent of the heavy oil can be recovered because the sections of the strata containing heavy oil located at a distance from the channels flowed through by the steam are not heated and accordingly their heavy oil contents are not rendered flowable. This phenomenon of the blowing through of the steam is known in the art as "override" or "fingering".
U.S. Pat. No. 3,881,550 describes the utilization of solvents which can be manufactured at the oil field in an inexpensive way and by means of which the viscosity of the heavy oil may be lowered. According to the disclosure of this patent specification the solvents for the heavy oil are injected at a high temperature and consequently lie on top of the oil shale or tar sand strata and accordingly no complete mixing and dissolving of the heavy oil takes place.
The prior art also includes:
(a) above ground processing after mining tar sands or shale from depths of 200 to 1000 feet or for producing below ground retorts, e.g. by electropneumatic or electrolytic mining or fracturing as disclosed in U.S. Pat. Nos. 3,696,866 (Dryden/Bureau of Mines) granted Oct. 10, 1972, 3,103,975 (Hanson/Dow) granted Sept. 17, 1973, and 4,120,776 (Miller, Univ. of Utah) granted Oct. 17, 1978, tailored to Utah sands; see also 4,160,720;
(b) means for exploding shale or sands underground and drawing oil from resultant rubble chambers, e.g. as disclosed in U.S. Pat. Nos. 3,578,080 (Closmann/Shell Oil) granted May 11, 1971; 3,692,110 (Grady/Cities Service) granted Sept. 19, 1972; 3,698,478 (Parker/Phillips Petroleum) granted Oct. 17, 1972; 4,061,190 (Bloomfield/NASA) granted Dec. 6, 1977 (laser retorting);
(c) propagation of pulsating energy waves for heating oil, e.g. as disclosed in U.S. Pat. No. 3,718,186 (Brandon) granted Feb. 27, 1973,
(d) variations of electro-conductive, inductive or rf heating as disclosed in U.S. Pat. No. 3,848,671 (Kern/Arco) granted Nov. 19, 1974 [see also Kern's 1975 U.S. Pat. Nos. 3,862,662, 3,874,450 and 3,920,072]; 3,948,319 (Pritchett/Arco) granted Apr. 6, 1976; 3,972,372, 3,989,107 and 4,008,761 and 2 Fisher) granted Aug. 3, 1976, and Feb. 22, 1977 [see also 4,049,053]; 4,010,799 (Kern/Petro-Canada, Imperial Oil, Cities Service) granted Mar. 8, 1977; Raytheon's U.S. Pat. Nos. 4,140,179 granted Feb. 20, 1979, 4,135,579 granted Jan. 23, 1979, and 4,193,451 and 4,196,329 granted Mar. 18 and Apr. 1, 1980;
(e) variations of pressures, steam or water injection cycles or production, injection well (and in some instances separate electrode well) spacings and arrangements, e.g. as disclosed in U.S. Pat. Nos. 4,084,637 (Todd/Petro Canada, Cities Service, Imperial Oil) granted Apr. 18, 1978; 3,946,809 (Hagedorn/Exxon) granted Mar. 30, 1976; 3,958,636 (Perkins/Arco) granted May 25, 1976; 4,133,382 (Cram/Texaco) granted Jan. 9, 1979;
(f) in situ gas generation; e.g. as in U.S. Pat. Nos. 4,037,655 and 4,199,025 (Carpenter/Electro Flood Co.) granted July 26, 1977, and Apr. 22, 1980;
(g) in situ combustion or dielectric heating, e.g. in U.S. Pat. No. 2,818,118 (Dixon/Phillips Petroleum) granted Dec. 31, 1957 ]see also 2,889,882, 2,994,377] and 4,140,180 and 4,144,935 (Bridges/I.I.T.) granted Feb. 20 and Mar. 20, 1979;
(h) complex means for analysis of flooding progress as disclosed e.g. in U.S. Pat. No. 4,085,798 (Schweitzer et al/Schlumberger) granted Apr. 25, 1978, and references cited therein.
(i) variations of solvent treatment e.g. as in U.S. Pat. No. 4,141,415 (Wu/Texaco) granted Feb. 27, 1979;
(j) electrical heating as in U.S. Pat. Nos. 3,507,330, 3,547,193, 3,620,300, 3,605,888, 3,642,066 (Gill et al/T.E.C.).
The diversity and intensity of the underlying development efforts (and incidental patent activity illustrated above) show the high economic stakes and long felt needs (substantially unfulfilled or only partially fulfilled, as illustrated by cross-critiques in the introductions of the various patents above) for economic, effective and practical oil recovery processes usable in shale and/or tar sand regions.
It is a principal object of this invention to provide oil recovery method and apparatus fulfilling one or more of such needs.
It is a further particular object of this invention, consistent with the first stated object, to suppress overriding (aka channeling or fingering).
It is a further particular object of this invention, consistent with the first stated object, to avoid problems of well clogging.
It is a further particular object of this invention, consistent with the first stated object, to limit the need for expensive or complex equipment.
It is a further particular object of this invention, consistent with the first stated object, to limit the number of maintenance cycles or the extent of interference with production occasioned by such cycles.
It is a further particular object of this invention, consistent with the first stated object, to more effectively utilize solvents in oil recovery and to lower critical specifications or cost of solvent usage.
It is a further particular object of this invention, consistent with the first stated object, to provide step by step working of an area for efficient usage of limited equipment resources.
It is a further particular object of this invention, consistent with the first stated object, to provide simple and economic means for process monitoring and control.